Multi-point link aggregation spoofing

ABSTRACT

A system with at least one, and preferably at least two, end devices that operates according to a point-to-point protocol such as the IEEE standard 802.3ad. The two end devices communicate with each other through a trunk cluster formed from a plurality of cluster devices. Each of the cluster devices has a synchronization means for configuring all of the cluster devices with a same logical identity to communicate with the end device according to the point-to-point protocol as if all of the cluster devices were a single device.

RELATED APPLICATIONS

This is a Continuation of application Ser. No. 09/493,563 filed Jan. 28,2000, now U.S. Pat. No. 6,687,751 and the entire disclosure of thisprior application is considered to be part of the disclosure of theaccompanying application and is hereby incorporated by referencetherein.

FIELD OF THE INVENTION

The present venture relates to computer network communication, and inparticular to combining a plurality of cluster devices to operate as asingle device and increase bandwidth in a point-to-point protocol suchas the Institute of Electrical and Electronics Engineers (IEEE) standard802.3ad for multiple Ethernet links.

BACKGROUND OF THE INVENTION

The 802.3ad standard issued by the IEEE specifies how to use multipleEthernet links to make a logical point-to-point connection. Thisstandard is published by the IEEE and is available from theirheadquarters, 345 East 47^(th) New York, N.Y. 10017. The IEEE is a wellknown organization to those skilled in the art of computer networkcommunication. The standards of the IEEE are readily available andunderstandable to those skilled in the art of computer networkcommunication. The IEEE standard 802.3ad is hereby incorporated byreference, as well as any portions of the entire 802 standard that maybe relevant to 802.3ad. It is expected that those skilled in the artwill be able to build a device that can adhere to the IEEE 802.3adstandard and meet the PICS performance in section 43B.6 of the standard.The present invention also relates to other point-to-point protocols andis not limited to the IEEE 802.3ad standard.

The IEEE 802.3ad standard assumes that the points of the connection aresingle devices and defines an optional Link Aggregation sublayer for usewith CSMA/CD (carrier sense multiple access/collision detection) MACs(Media Access Control). Link Aggregation allows one or more links to beaggregated together to form a Link Aggregation Group, such that a MACClient can treat the Link Aggregation Group as if it were a single link.To this end, it specifies the establishment of DTE to DTE logical links,which consist of N parallel instances of an 802.3 link, all of which arefull duplex point-to-point links operating at the same data rate.

U.S. Pat. No. 6,195,351 filed Jan. 28, 1998 discloses a Logical SwitchSet (LSS) comprising two or more switches that act as a single packetforwarding device with specific connection rules. The single packetforwarding device is a single logical unit. The LSS may be used aseither a redundant switch set (RSS) or as a Load Sharing Switch Set(LSSS). The maximum throughput of the LSSS increases with eachadditional switch. A LSSS can only interconnect with the other devicesvia trunked links that contain at least one physical connection to eachswitch. The RSS may include a trunk link connection and a resilient linkconnection. U.S. Pat. No. 6,195,351 is hereby incorporated by reference.

U.S. Pat. No. 6,195,349 filed Jan. 28, 1998 discloses a packet basedhigh speed mesh forming a trunk cluster. The trunk cluster isconstructed with a set of loosely coupled switches, a configurationprotocol, trunked network interfaces, and optionally a reachabliltyprotocol. The trunk cluster provides a Logical LAN service. Each switchin the trunk cluster provides a single “shared LAN” by interconnectingtwo or more links. The edge devices attached to the links run a trunkconfiguration protocol. These attached edge devices view the trunkedports as if trunked ports are connected to a shared LAN with multipleother attached devices. U.S. Pat. No. 6,195,349 is hereby incorporatedby reference.

U.S. Pat. No. 6,347,073 filed Apr. 29, 1998 discloses a plurality ofindependent control lines used by I/O modules to determine which switchof a redundant switch set is the active or primary switch. Each line isdriven by a different source. Each of these control lines are driven byone of a plurality of judges and each judge can read the other controllines which they are not driving. All the I/O modules can only read thecontrol lines. Each judge makes a decision as to which switch should bethe primary switch. Each decision is conveyed using the control lines.The I/O modules use these control lines to direct a multiplexer of therespective outside node to connect to the primary switch. A majorityrules algorithm is used to always obtain the correct result in the faceof a single error. U.S. Pat. No. 6,347,073 filed Apr. 29, 1998 is herebyincorporated by reference.

U.S. Pat. No. 6,058,116 filed Apr. 15, 1998 discloses an arrangement oftrunk clusters and a method for interconnecting trunk clusters whereinthe interconnection method has no single point of failure, the bandwidthbetween trunk clusters is not limited by the throughput of a singleswitch, and faults are contained within each trunk cluster. A trunkedinterconnection structure is provided between trunk clusters. Eachswitch of a trunk cluster has a logical port connected to a trunkedport. The trunked port or trunk port provides a physical connection toeach trunk switch of another trunk cluster. Each trunk switch of theanother trunk cluster has a logical port connected to a trunked portwhich in turn has physical connections to each switch of the first trunkcluster. Trunked interconnections isolate faults to a single trunkcluster, there is no single point of failure and the total throughput isnot limited to any single switches capacity. This always provides asingle loop free path from one trunk cluster to the other or others.Multiple trunk clusters may be interconnected using point-to-pointconnections. A high throughput campus interconnect trunk cluster can beused to connect each building data center trunk cluster. U.S. Pat. No.6,058,116 filed Apr. 15, 1998 is hereby incorporated by reference.

SUMMARY AND OBJECTS OF THE INVENTION

It is a primary object of the present invention to provide a pluralityof network devices as representing a single point device of thepoint-to-point protocol, such as the IEEE 802.3ad standard. The presentinvention makes it possible to have one or both of the points of theIEEE 802.3ad standard be multiple devices. The multiple devices of thepresent invention are configured to behave as a single point in such away that the multiple devices still adhere to the 802.3ad standard. Thusthe multi device point can be seamlessly connected to a conventionalsingle device that supports the 802.3ad specification.

The present invention accomplishes this by providing a system with atleast one, and preferably at least two, end devices that operateaccording to the point-to-point protocol. The two end devicescommunicate with each other through a trunk cluster formed from aplurality of cluster devices. More than one of the cluster devices arein communication with more than one of the end stations, and the clusterdevices identify connected end stations. The cluster devices share theidentity of the connected end stations and commonly connected endstations. Each of the cluster devices has a synchronization means forconfiguring each the cluster device in communication with the commonlyconnected end stations to use a same logical identity for thepoint-to-point protocol.

The synchronization means of each cluster device exchanges individualsynchronization state data with the synchronization means of the othercluster devices. Each synchronization means then configures therespective cluster device dependent on the exchanged synchronizationstate data and its own synchronization state data. If there are only twosubstantially similar cluster devices, both synchronization means canuse the same algorithms to determine respective configurations. Sinceboth synchronization means will apply the algorithms to the same data,the configurations will be identical and compatible.

For a trunk cluster with a large number of cluster devices, and/orsignificantly different cluster devices, each of the synchronizationmeans can include algorithms and communicate with each other to operateone of the synchronization means as a master synchronization means(MSM). The master synchronization means determines clustersynchronization data needed for configuring and operating the individualcluster devices in order for the individual cluster devices tocommunicate with the end device according to the IEEE standard 802.3ad.The master synchronization means transfers the cluster synchronizationdata to the plurality of cluster devices in the trunk cluster. Eachsynchronization means configures a respective cluster device accordingto the cluster synchronization data.

The master synchronization means can be chosen based on thesynchronization state data of the individual cluster devices, or theelection of the master synchronization means can be predetermined, suchas by a system operator. Likewise the cluster synchronization data canbe determined from the individual synchronization data of the clusterdevices, or the cluster synchronization data can be predetermined, suchas by a system operator.

The cluster devices communicate with the end devices throughcommunication links. The communication of the individual synchronizationdata and the cluster synchronization data is performed through anintra-cluster interconnect (ICI.). The intra-cluster interconnect can beformed from dedicated network links between the cluster devices, or theintra-cluster interconnect can be included in the communication carriedby the communication links. In either embodiment, each device in thetrunk cluster has a unique identification for the intra-clusterinterconnect communication. The communication across the intra-clusterinterconnect is based on the unique identification of the individualcluster devices. The design of the intra-cluster interconnect is wellwithin the ability of those skilled in the art of computer networkcommunication, and the exact design of the intra-cluster interconnect isnot part of the scope of the present invention.

In a preferred embodiment, each of the cluster devices has means foroperating according to be IEEE standard 802.3ad, and this means isconfigurable by the synchronization means of the present invention. Thepresent invention is not limited to two single end devices communicatingthrough a trunk cluster, but instead a plurality of trunk clusters couldcommunicate with each other according to the 802.3ad standard, whereeach trunk cluster appears as a single point device according to the802.3ad standard.

The present invention is an improvement over the 802.3ad standard, sinceadditional bandwidth can be added to an end device by taking advantageof additional network devices. In the 802.3ad standard, additionalbandwidth can only be added by adding additional communication linksthat directly connected two devices. If one of the devices has lessports than the other, bandwidth of the device having more ports iswasted with the IEEE standard 802.3ad. With the present invention aplurality of cluster devices having a small number of ports can beconnected to a single 802.3ad device to take full advantage of all theports of the single 802.3ad device. The present invention providesefficient configuration of a computer network which will increase therate at which a computer network can transfer data, and/or reduce theequipment needed to insure an adequate data rate. The plurality ofnetwork devices representing a single 802.3ad device also increasesreliability of a network by eliminating a single point of failure.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic diagram of computer network devices operatingaccording to the 802.3ad standard;

FIG. 2 is a schematic diagram of a trunk cluster communicating with enddevices according to the 802.3ad standard;

FIG. 3 is an enlarged schematic diagram of a link aggregation sublayerfor configuring the cluster devices to operate according to the 802.3adstandard;

FIG. 4 is a schematic diagram of the interaction between thesynchronization means of the different cluster devices.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, and in particular to FIG. 1, the 802.3adstandard applies to a computer network where a single 802.3ad device 1Acommunicates with another 802.3ad device 1B through a plurality ofcommunication links 3A. The standard allows the communication betweendevices 1 to use more than one communication link 3, and thus increasesthe bandwidth and the data rate between two of the devices 1. Howeverthe 802.3ad standard is not designed to have one network device 1Acommunicate with another network device 1C through a plurality ofcommunication links 3 connected to a plurality of in between devices 7as shown in FIG. 2. The 802.3ad standard is therefore unable to takeadvantage of multi-home connections and any unused capacity that mightbe available on other devices that have similar connections. Each single802.3ad device inherently becomes a single point of failure.

FIG. 2 shows two 802.3ad devices 1A, 1C which can be consideredequivalent to the end devices 1A, 1C of FIG. 1. The end devices 1A, 1Ccommunicate through communication links 3A, 3C and through a trunkcluster 5 which has been configured to appear to the end devices 1A, 1Cas a single 802.3ad device such as 802.3ad device 1B in FIG. 1. Insidethe trunk cluster 5 are a plurality of cluster devices 7. Each clusterdevice 7 is connected to each of the end devices 1A, 1C by one of thecommunication links 3A, 3C. It is also possible for the cluster devices7 to also communicate with other miscellaneous network devices 9. Theend devices 1 can also communicate with the other miscellaneous networkdevices 9. The miscellaneous network devices are shown to indicate thatthe present invention can be incorporated into a larger computer networkand that the present invention is not required to form the entirecomputer network.

Each cluster device 7 includes a plurality of ports 11. The ports 11 areconnected to the other network devices by the communication links 3.Cluster device 7B is shown connecting to the end devices 1A, 1C by aplurality of ports 11A and 11C in accordance with the 802.3ad standard.The two ports 11A in cluster device 7B form a logical or virtual port.Each port 11 in a logical port is connected to a link aggregationsublayer 25. The present invention combines ports 11A in cluster devices7A and 7C also into the logical port of cluster device 7B, and theseports have link aggregation sublayers 25. The same combining of ports11C into a logical port with a link aggregation sublayer 25 is alsoshown in FIG. 2.

FIG. 3 is an expansion of the lower bottom portion of FIG. 2. Each port11 has a port ID and a port priority. Each aggregation sublayer 25includes a device controller 13 which controls how the cluster device 7operates. The device controller 13 preferably is an 802.3ad means foroperating the cluster device according to 802.3ad standard. Eachaggregation sublayer 25 also includes an aggregator 15 in accordancewith the 802.3ad standard. Aggregators 15 can be assigned a 16 bit key.Those aggregators 15 that have the same key on each cluster device 7 areconsidered to be a component of a trunk cluster wide cluster aggregator.The aggregators 15 will appear to the end device 1 as a singleaggregator.

FIG. 3 also shows that each cluster device 7 also includessynchronization means 17. The synchronization means 17 configures therespective link aggregation sublayer 25 and in particular the respectivedevice controller 13, to cause all of the cluster devices 7 to appear tothe end device 1 as a single 802.3ad device. The synchronization means17 of each of the cluster devices 7 provides what is known in the art,as a plurality of cluster devices 7 “spoofing” a single 802.3ad device.

As shown in FIG. 4, the synchronization means 17 of each linkaggregation sublayer 25 in each cluster device 7 exchange individualsynchronization data and cluster synchronization data over or through anintra-cluster interconnect. The intra-cluster interconnect can either beformed of dedicated network links 21 or the intra-cluster interconnectcan be included in the communication passing through communication links3C.

Each synchronization means 17 communicates with the synchronizationmeans 17 in the other cluster devices 7 through the ICI 21. Eachsynchronization means 17 also can communicate and control the functionsin its respective cluster device 7 that are required to meet the 802.3adspecification.

Each device in the cluster has an associated 8 octet binary numbercalled the system aggregation priority as specified in section 43.6.1 ofthe 802.3ad specification. Through the ICI, the synchronization means 17in the cluster device 7 will determine which cluster device 7 has thelowest numerical value for the system aggregation priority. The clusterdevice 7 with the lowest numerical value has the highest priority and ispreferably chosen as the Master Synchronization Means (MSM) 23.

The Master Synchronization Means (MSM) 23 does the following:

1. Chooses a cluster Identification. This Id, which is 6 bytes long, hasthe same format and meets the same specifications as the system Id forindividual devices. To do so, the MSM may collect the system Identifiersof the active cluster devices 7 over the ICI and by choosing among oneof them. The MSM may also read the value from a database configured by auser or system operator.

2. Chooses a cluster priority. This value, which is 2 bytes long, hasthe same format and meets the same specifications as the system priorityfor individual devices. To do so it may collect the system priorities ofthe active devices in the cluster over the ICI and choose among one ofthem. It may also read the value from a database configured by a user.

3. Communicates the chosen cluster Identification value and clusterpriority to the synchronization means 17 in other devices.

4. Chooses the cluster_aggregator-MAC-Address for each clusteraggregator. To do so the MSM may collect the aggregator-MAC-Addresses ofthe aggregators 15 that make up the cluster aggregator and choose avalue amongst them. It may also read the mac addresses from a databaseconfigured by a user.

5. Chooses the port ID's that each device 7 in the cluster is to use forits ports 11. These port ID's which are 2 bytes long have the sameformat and meet the same specifications as the Port Id for individualdevices 1, 7. To do so it may collect the Port ID's of the activedevices 7 in the trunk cluster 5 over the ICI. It may also read thevalues from a database configured by a user.

6. Chooses the port priority to be used for each port 11 on each device7 in the trunk cluster 5. These port priorities which are 1 byte longhave the same format and meet the same specifications as the Portpriority for individual devices 1, 7. To do so the mastersynchronization means 23 may collect the Port priorities of the activedevices 7 in the trunk cluster 5 over the ICI. The mastersynchronization means 23 may also read the values from a databaseconfigured by a user.

7. Communicates the chosen port ID's and port priorities for each port11 on each device to the synchronization means 17 in other devices 7 inthe trunk cluster 5.

8. Receives lists of actor keys, partner keys, partner system ID's andconstraint details from the synchronization means 17 in other devices 7.After having received a list from each active synchronization means 17,the master synchronization means 23 selects:

a. which ports 11 are to go into the STANDBY state

b. which ports 11 should change their key values and what key value itshould be changed to.

9. Communicate the decisions from the above operation 8 to thesynchronization means 17 of the other devices.

10. Communicates to the synchronization means 17 of the other clusterdevices 7 when the other cluster devices 7 are allowed to change thesynchronization bit in the Link Aggregation Control Protocol Data Unit(LACPDU) to In-Sync. The master synchronization means 23 will send thiscommand, when it has had sufficient communication with eachsynchronization means 17 or has decided that a synchronization means 17is not available or functioning.

Each synchronization means 17 does the following:

1. Periodically sends messages over the ICI containing its systemaggregation priority to indicate that it is healthy. Tracks thefunctioning of all the synchronization means 17 by tracking thesemessages. If the master synchronization means 23 is not heard, selectthe synchronization means 17 with the lowest value for the systemaggregation priority to be the new master synchronization means 23.

2. May collect one or more of the following: the system Id, systempriority, Port ID's, Port priority and aggregator-MAC-Addresses andcommunicate them to the master synchronization means 23.

3. Commands the functions that set the synchronization Bit in the LACPDUto keep it low until the highest priority synchronization means 17communicates to the synchronization means 17 that the bit is allowed togo high. This effectively means that the Mux State on the device staysin the Out-of Sync state.

4. Commands the functions that use the system Identifier to meet the802.3ad standard to use the cluster Identifier. This includes functionsthat construct the Marker PDUS, Marker Response PDUs and LACPDU in itsdevice and functions that look for loopbacks.

5. Commands the functions that use the system priority to meet the802.3ad standard to use the cluster priority. This includes functionsthat construct the Marker PDUS, Marker Response PDUs and LACPDU in itsdevice.

6. Commands the functions that use the aggregator-MAC_Address to meetthe 802.3ad standard to use the cluster_aggregator-MAC-Address for eachaggregator 15 that is a member of a trunk cluster 5. The aggregator 15must communicate to the MAC Client the cluster_aggregator_MAC-Address.

7. Commands the functions that use the Port ID's and Port priorities tomeet the 802.3ad standard to use the Port ID's and Port prioritiesallocated by the master synchronization means 23 to its device instead.

8. Commands the functions that may exist in the cluster device 7 tohandle limited aggregation capability as described in 43.6.2 to:

a. not change any port's operational key values unless so commanded bythe highest priority synchronization means 23;

b. to sends its device's synchronization means 17 the port ID's, partnerkeys and partner system ID's of those ports 11 that can't all aggregatedue to an aggregation constraint;

c. to keep the ports 11 that can't all aggregate in the Out-of-syncstate until the synchronization means 17 indicates which ports 11 are tobecome SELECTED and which STANDBY.

9. Communicates the constraint details, actor keys, partner keys,partner system ID's and port ID's of those ports 11 that can't fullyaggregate due to constraints to the master synchronization means 23.

10. When the master synchronization means 23 indicates which ports of aconstrained aggregation should change their key values and which shouldgo into STANDBY communicate to the constraint function to:

a. change the operational key values of the ports 11 to the valuesindicated by the master synchronization means 23;

b. set the ports 11 that are not to go into the STANDBY state into theIn_Sync state.

In some cases it is desirable that there are aggregation constraintsthat apply to the whole trunk cluster 5. If the devices 7 in the trunkcluster 5 are bridges for example, there are conditions under which itmay be necessary for all the communication links 3 to one or moredevices to not be used. The master synchronization means 23 can be awareof these rules and can decide which ports 11 on which cluster devices 7are not to be used. It can send a command to the synchronization means17 of the other devices to indicate that the not-to-be used ports 11 areto go into the STANDBY state.

The synchronization means 17 in the devices will command the functionsthat control the port state to go into the Out-of-Sync state and toindicate this by setting the synchronization bit to 0.

If there are only two cluster devices 7, it may be easier to not choosea master synchronization means 23. A reliable communication can be setup much like the one designed for the 802.3ad specification, wherebyeach synchronization means 17 knows the state of the othersynchronization means 17. Each synchronization means 17 will send to theother synchronization means 17, what it would have sent to the mastersynchronization means 23, plus some additional maintenance information.It is then possible for each synchronization means 17 to deduce on itsown what the master synchronization means 23 would have deduced. Theneach synchronization means 17 can configure the functions in itsrespective cluster device 7 as it would have if a master synchronizationto and means 17 was chosen.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:
 1. A method for network communications with an endstation operating using a point-to-point protocol, the method comprisingthe steps of: providing a plurality of cluster devices, said clusterdevices being in communication with the end station, each of saidcluster devices identifying the end station; operating said clusterdevices to communicate with the end station using the point-to-pointprotocol; communicating between each of said cluster devices todetermine that each said cluster device is connected to the same endstation; configuring a logical identity for each of said cluster devicesconnected to the end station; configuring the point-to-point protocol ofeach of said cluster devices to operate using said logical identity andhave each of said cluster devices appear to the end station as saidlogical identity.
 2. A method in accordance with claim 1, furthercomprising: providing a plurality of end stations connected to saidcluster devices, more than one of said cluster devices being connectedto more than one of the end stations; identifying which of said clusterdevices are connected to common end stations; configuring a commonlogical identity for said cluster devices connected to the common endstations; configuring the point-to-point protocol of each of saidcluster devices connected to the common end stations to operate usingsaid common logical identity and to have each of said cluster devicesappear to the common end stations as said common logical identity.
 3. Amethod in accordance with claim 1, wherein: the point-to-point protocolis IEEE standard 802.3ad; the end devices is a 802.3ad device operatingaccording to IEEE standard 802.3ad; said configuring of the logicalentity and said configuring of the point-to-point protocol causes eachof said cluster devices appear to the common end station as said logicalidentity according to IEEE standard 802.3ad.
 4. The method in accordancewith claim 3, wherein: one of said cluster devices includes a mastersynchronization means (MSM) and determines cluster sync data foroperating said cluster devices to communicate with said 802.3ad deviceaccording to the IEEE standard 802.3ad; said MSM transfers said clustersync data to said plurality of cluster devices during saidcommunicating; said configuring of the point-to-point protocol of eachof said cluster devices is according to said cluster sync data.
 5. Themethod in accordance with claim 4, wherein: said cluster devicesexchange individual sync data with other said cluster devices and saidcluster devices choose said MSM based on said individual sync data. 6.The method in accordance with claim 5, wherein: said MSM determines saidcluster sync data based on individual sync data of each of said clusterdevices.
 7. The method in accordance with claim 3, wherein: each saidcluster device includes 802.3ad means for individually operating arespective said cluster device according to the IEEE standard 802.3ad,said configuring of the point-to-point protocol including configuringsaid 802.3ad means.
 8. The method in accordance with claim 1, wherein:said communicating between each of said cluster devices is through anintra-cluster interconnect (ICI) providing communication between saidcluster devices.
 9. The method in accordance with claim 8, wherein: saidICI includes dedicated network links between said cluster devices. 10.The method in accordance with claim 9, wherein: said ICI provides saidcommunication between said cluster devices through third party devices.11. The method in accordance with claim 8, wherein: said communicationbetween said end stations and said cluster devices is throughcommunication links, said ICI provides said communication between saidcluster devices through said communication links.
 12. The method inaccordance with claim 1, wherein: said communicating between each ofsaid cluster devices includes exchanging individual sync data withanother of said cluster devices; said configuring of the point-to-pointprotocol of each of said cluster devices is dependent on respective saidsync data and said sync data from said another cluster device.
 13. Amethod for operating a network cluster with an end station using apoint-to-point protocol, the method comprising: providing a plurality ofcooperating cluster devices; connecting each of said cluster devices tothe end device with a plurality of trunk links to form a cluster;providing a coordinating link between the cooperating cluster devices inthe cluster; and coordinating and synchronizing each of the plurality ofcluster devices through the coordinating link such that each of theplurality of cluster devices behave as a single point device in thepoint-to-point protocol of the end station.
 14. A method for operating asingle cluster device in a cluster device arrangement communicating withan end station using a point-to-point protocol, the method comprisingthe steps of: receiving at the single cluster device point-to-pointprotocol information from the cluster device arrangement; coordinatingand synchronizing the single cluster device with the cluster devicearrangement to have the single cluster device and the cluster devicearrangement operate such that the single cluster device and the clusterdevice arrangement behave as a single point device in the point-to-pointprotocol of the end station; operating the single cluster device tocommunicate with the end station using the point-to-point protocol incoordination with the cluster device arrangement.